1. Technical Field
The present disclosure relates to a light emitting diode (LED).
2. Description of the Related Art
LEDs are semiconductors that convert electrical energy into light. Compared to conventional light sources, LEDs have higher energy conversion efficiency, higher radiance (i.e., they emit a larger quantity of light per unit area), longer lifetime, higher response speed, and better reliability. LEDs also generate less heat. Therefore, LED modules are widely used as light sources in optical imaging systems, such as displays, projectors, and so on.
A typical LED commonly includes an N-type semiconductor layer, a P-type semiconductor layer, an active layer, an N-type electrode, and a P-type electrode. The active layer is located between the N-type semiconductor layer and the P-type semiconductor layer. The P-type electrode is located on the P-type semiconductor layer. The N-type electrode is located on the N-type semiconductor layer. Typically, the P-type electrode is transparent. In operation, a positive voltage and a negative voltage are applied respectively to the P-type semiconductor layer and the N-type semiconductor layer. Thus, holes in the P-type semiconductor layer and photons in the N-type semiconductor layer can enter the active layer and combine with each other to emit visible light.
However, the extraction efficiency of LEDs is low because the contact area between the N-type semiconductor layer and the active layer is not large enough. Thus the electron-hole recombination density is low, and the photons in the LED are sparse, thereby degrading the extraction efficiency.
What is needed, therefore, is a light emitting diode which can overcome the above-described shortcomings.